Unravelling the Potamonautes lirrangensis (Rathbun, 1904) species complex (Potamoidea: Potamonautidae), with the description of two new species

The taxonomic status of the widely distributed freshwater crab Potamonautes lirrangensis (Rathbun, 1904) sensu lato is revised because morphological and molecular evidence indicates that this taxon is a complex comprising more than one species. Four taxa are now recognized: Potamonautes lirrangensis (Rathbun, 1904) s. str. and P. kisangani sp. nov. from the Middle Congo River in Central Africa, P. amosae sp. nov. from the drainages of Lakes Kivu and Tanganyika, and P. orbitospinus (Cunnington, 1907) from Lake Malawi which had been previously synonymised with P. lirrangensis s. lat. Diagnoses, illustrations and distribution maps are provided for each of these taxa and they are compared to similar species from Central and Southern Africa.


Introduction
This work focuses on the taxonomic status of the widely distributed species Potamonautes lirrangensis (Rathbun, 1904) s. lat., which has a reported range that includes the Middle Congo River (Rathbun 1904,  (Cunnington, 1907). The black star shows the type locality. See text and Table 2 for exact localities.
to establish the beginning of the adult size range for male specimens. The terminology is adapted from Cumberlidge (1999) and the higher classifi cation used follows that of Ng et al. (2008).

Molecular and phylogenetic analyses
Tissue was harvested from either the gills or the ambulatory legs of ethanol preserved specimens. DNA was extracted using a DNeasy kit (Qiagen, Hilden, Germany), following the protocol of the manufacturer. One mitochrondrial (16S rRNA) and one nuclear (histone 3, H3) locus were sequenced, using the primers 16SA and 16SB (Palumbi et al. 1991), and H3AF and H3AR (Colgan et al. 1998), as reported in Daniels et al. (2015). PCR reactions were conducted in 25 μL volumes, including 12.5 μL of MyTaq mastermix (Bioline, London), 0.5 μL of each primer (10 mM), 11 μL molecular grade water, and 1 μL of template DNA (1:10 dilution of eluted DNA). PCR conditions were as follows: 1 minute at 95°C, then 35 cycles of 95°C for 30 s, 50°C for 30 s and 72°C for 1 minute, followed by 72°C for 5 minutes. Amplification success was checked on 1% agarose gel. Purifi cation and sequencing of the PCR products was outsourced to either Macrogen (Seoul, Korea) or Eurofi ns Genomics (Wolverhampton, UK). Sequences were checked using Chromas ver. 2.6 (Technelysium Ltd, Brisbane), and novel sequences have been deposited in GenBank (Table 2).
Sequences were aligned using ClustalW (Thompson et al. 2003), and concatenated in SequenceMatrix (Vaidya et al. 2011). The phylogenetic analyses utilised both the 16S and H3 genes. Maximum Likelihood (ML) analyses were conducted in IQ-TREE ver. 2.12 (Minh et al. 2020), on the IQ-TREE webserver, using an automatic model selection including the 16S locus as one partition, and each codon position of the H3 genes as separate partitions (Chernomor et al. 2016). Branch support was estimated from 1000 Table 1. History of the description of the fi rst gonopod (G1) of specimens of Potamonautes lirrangensis (Rathbun, 1904) s. lat. with the revised identifi cations in the present work.
Non-type NMU TRW 1972.05 Cumberlidge & Meyer (2011: fi g. 7a-b) Malawi Lake Malawi P. orbitospinus (Cunnington, 1907) P. lirrangensis (Rathbun, 1904) s. lat. ultrafast bootstrap replicates (Hoang et al. 2018). Only bootstrap proportions > 70% were regarded as strongly supported. Bayesian inference (BI) analyses were conducted in BEAST ver. 2.6.3 (Bouckaert et al. 2019), using the same partitions and equivalent models as in the ML analyses, and a chain length of 50 million generations. Every 1000 th tree was sampled, and the fi rst 50% of trees were discarded as burn-in. Posterior probability branch support was calculated using Tree Annotator (part of the BEAST package), with values of > 0.9 regarded as strongly supported. Trees were visualised using FigTree ver. 1.4.4 (http://tree.bio.ed.ac.uk/software/fi gtree/), and the Bayesian maximum credibility tree is shown.

Range area calculations
The updated geographic distribution of P. lirrangensis s. str. and P. kisangani sp. nov. (Fig. 1), P. amosae sp. nov. (Fig. 3), and P. orbitospinus (Fig. 2) are provided, and the extent of occurrence (EOO) for each species was calculated using GeoCAT (Bachman et al. 2011) as the area contained within the minimum convex polygon around all sites of present occurrence. The area within the EOO that is actually occupied by the taxon (the area of occupancy; AOO) was estimated using GeoCAT as the sum of the area occupied within a 2 × 2 km grid overlaid around each locality. Family Potamonautidae Bott, 1970Subfamily Potamonautinae Bott, 1970Genus Potamonautes MacLeay, 1838 Potamonautes lirrangensis (Rathbun, 1904) Ng et al. 2008: 171 (partim).

Material examined
Holotype (

Description
See Diagnosis.

Size
Medium-sized species, adult at CW 43 mm.

Colour
The preserved specimen from Liranga is uniformly light brown.

Distribution
The revised distributional range of P. lirrangensis s. str. (Fig. 1) now comprises just the Middle Congo River: Liranga (not 'Lirranga' as implied from the specifi c epithet) in the République du Congo. This species now excludes specimens formerly identifi ed as P. lirrangensis s. lat. from Kisangani in the D.R. Congo (Fig. 1), rivers near Kigoma draining into Lake Tanganyika, in Tanzania, Lake Tanganyika in Zambia (Fig. 3), and Lake Malawi in Malawi (Fig. 2).

Ecology
The type locality of P. lirrangensis s. str. in the Middle Congo River (Liranga) lies in the Sudanic Congo-Oubangi Ecoregion (Freshwater Ecoregions Of the World (FEOW #535) (Thieme et al. 2005;Abell et al. 2008). This is more than 1000 km from Kisangani where Potamonautes kisangani sp. nov. is found in the Upper Congo Rapids Ecoregion (FEOW # 539), which indicates that the habitats of these 2 taxa are different, despite both being located in the Middle Congo River. Interestingly, these 2 taxa are separated by a third ecoregion, the Cuvette Centrale (FEOW #537).

Comparisons
Taxonomically important characters of the male cheliped, thoracic sternum, and gonopods, and the colour when alive, together with DNA data for P. lirrangensis s. str. will not be available until topotypal material is collected that includes an adult male. The carapace of the female type specimen from Liranga was illustrated by Capart (1954: fi g. 28) and photographed by Rathbun (1904: pl. 14 fi g. 8) and (together with the cheliped carpus) have been included in the present study (Figs 4A, 7A).
The lateral margin of the exorbital tooth of P. lirrangensis s. str. from Liranga ( Fig. 4A) is similar to that of P. kisangani sp. nov. from Kisangani (Fig. 4B;Rathbun 1904: fi g. 8a) and is angled outward at 45° to the midline of the carapace and is straight and neither bulges outward (convex) nor curves inward (concave). This contrasts with that of P. amosae sp. nov. from Lake Kivu (Fig. 4C) and the Malagarasi River (Reed & Cumberlidge 2006: pl. 5a), where the lateral margin of the exorbital tooth is not straight and bulges distinctly outward (convex) before meeting the postfrontal crest. This also contrasts with P. orbitospinus from Lake Malawi (Fig. 4E) where the lateral margin of the exorbital tooth curves inward (concave) and is neither straight nor convex.
The identifi cations of specimens as P. lirrangensis s. lat. by a number of authors (Rathbun 1921;Chace 1942;Bott, 1955;Reed & Cumberlidge 2006;Cumberlidge & Meyer 2011) are all now considered unreliable because they confl ate characters from the 4 taxa that comprise the species complex under study here. Specifi cally, the descriptions of the male characters of P. lirrangensis s. lat. by the above authors combined characters from specimens from Kisangani, Lake Kivu, Tanzania, and Lake Malawi (Table 1).

Conservation status
The current IUCN extinction risk assessment of LC for P. lirrangensis s. lat. was based on the extremely wide range of that taxon (Cumberlidge 2018). The present work reduces the range of P. lirrangensis s. str. signifi cantly (Fig. 1), from an estimated extent of occurrence (EOO) of almost 1.5 million km 2 based on 58 localities, to a single locality that precludes the calculation of the EOO. This change will no doubt impact the conservation assessment of this species when it is revised.

Description
See Diagnosis.

Size
Large-sized species, adult at CW 53 mm, largest known specimen CW 66 mm.

Colour
The colour of living specimens from Kisangani D.R. Congo was provided by Rathbun (1921: 415). The dorsal carapace is either dark blue, dark green, or dark brown, the thoracic sternum is pink with blue/ gray tones, and the pleon is yellow/white. The fi xed and movable fi ngers of the chelae are dark brown/ black in recently preserved specimens ( Fig. 6A-B), while the arthrodial membranes of the chelipeds are vermillion (vivid red/orange).

Distribution
This species is only known from the vicinity of Kisangani in the D.R. Congo (Fig. 1).

Ecology
Kisangani lies in the Upper Congo Rapids Ecoregion (FEOW #539) (Thieme et al. 2005;Abell et al. 2008). The fi eld notes of Herbert Lang on the habitat of P. kisangani sp. nov. from Kisangani provided by Rathbun (1921: 415) indicate that although this species is found in large rivers, it favours shallow waters near river banks where drifting logs jam. At the Boyoma Falls near Kisangani these crabs were common above and below the cataracts, while in the Tshopo River crabs were abundant among the rocks and boulder fi elds above the Tshopo Falls, but were absent below the falls where the water was shallow and had a sandy substrate.

Comparisons
The epibranchial tooth and anterolateral margin of P. kisangani sp. nov. from Kisangani (Fig. 4B) and of P. amosae sp. nov. from Lake Kivu (Fig. 4C) and the Malagarasi River ( Fig. 4D; Reed & Cumberlidge 2006: pl. 5a) are similar in both species: the epibranchial tooth is a small granule that is followed by large granules lining the anterolateral margin. In contrast, the epibranchial tooth of P. lirrangensis s. str. from Liranga (Fig. 4A) and of P. orbitospinus from Lake Malawi (Fig. 4E) is pointed and as large as the other teeth lining the anterolateral margin.
The ischium of the third maxilliped of P. kisangani sp. nov. from Kisangani (Fig. 5A) and of P. orbitospinus from Lake Malawi (Fig. 5C) has a thin but distinct vertical sulcus, whereas this sulcus is faint and obscure in P. amosae sp. nov. from Lake Kivu (Fig. 5B) and the Malagarasi River (Reed & Cumberlidge 2006: pl. 5c-d).
The major chela has 3 large molars at the proximal ends of both fi ngers, with older specimens showing fusion of these teeth into a fl at surface of the fi xed fi nger in P. kisangani sp. nov. from Kisangani (Figs 6A-B, 8A) and in P. amosae sp. nov. from the Malagarasi River (CW 80.1 mm) (Fig. 6E-F; Reed & Cumberlidge 2006: pl. 5a fi gs 46-47), whereas the proximal parts of both fi ngers of the major chela in P. orbitospinus from Lake Malawi (Fig. 6G-H) has enlarged, rounded, separate (unfused) teeth.
The G1 TA in P. kisangani sp. nov. from Kisangani (Fig. 11A) and P. amosae sp. nov. from Lake Kivu ( Fig. 11B-D, F) and the Malagarasi River (Reed & Cumberlidge 2006: pl. 5c-d fi g. 152) is only slightly widened by a low dorsal lobe and the TA ends in either a straight, or only slightly upcurved tip. This contrasts with the G1 TA in P. orbitospinus from Lake Malawi, which is conspicuously widened by a high, rounded dorsal lobe (as wide as the TA width at the TA-SA junction) and the G1 TA ends in a strongly curved upwards tip (Fig. 12A-H).

Diagnosis
Exorbital tooth large forward-pointing spine; lateral margin of exorbital tooth lined by granules before meeting postfrontal crest; epibranchial tooth small, granular, followed by small granules lining anterolateral margin (

Etymology
The new species is named to honour the memory of Marilyn Suzanne Amos, of Mobile, Alabama, USA, who passed away during these studies. She was the mother of the second author (EJ). The specifi c epithet is used as a Latin noun in apposition. The vernacular name is Amos's crab.  (2021) 164 Fig. 9. Potamonautes amosae sp. nov., holotype, adult, ♂, CW 46.5 mm, from Lake Kivu, D.R. Congo (NHMUK 2018.306). A. Entire animal, dorsal view. B. Entire animal, ventral view. Scale bar = 11.3 mm.
Male pleon slim, triangular, telson narrow triangle with rounded apex, pleomeres Al-6 quadrate. G1 TA proximal third straight, not widened, margins parallel, at midpoint bent sharply outward at 60° angle to longitudinal axis of G1 SA; G1 TA ( Fig. 11B-E) widened by low dorsal lobe (⅓ TA width at TA-SA junction); tip straight, only slightly upcurved. G1 SA at junction with G1 TA with horizontal margin on ventral side, U-shaped indentation fi lled by conspicuous dorsal membrane on dorsal side. G2 TA long, fl agellum-like (Fig. 11F). Margins of G1 TA, SA lined by setae.

Size
Large species, adult size range between CW 50 to 80 mm.

Colour
Preserved specimens are uniformly light brown like the holotype, but the large adult female from the Malagarasi River in Tanzania has black pigmentation on both fi ngers of the chelae (Fig. 6E-F).

Distribution
Potamonautes amosae sp. nov. was collected from rocky areas of Lake Kivu in the D.R. Congo and Rwanda (Fig. 3). Lake Kivu is a relatively small (100 km long by 50 km wide), deep lake (depth 480 m) situated in the Albertine Rift of the Western Rift Valley. This lake is divided by the border between the D.R. Congo and Rwanda, with the large Idjwi Island lying in the D.R. Congo. The Ruzizi River drains south out of Lake Kivu and links it to the northern part of Lake Tanganyika in Burundi, but this species has not been recorded from this river. Potamonautes amosae sp. nov. is found along the eastern shores of Lake Tanganyika in localities associated with the Malagarasi River in western Tanzania (Capart 1952;Reed & Cumberlidge 2006;M. Mbalassa & S. Marijnissen pers. com.) where it fl ows through the Kigoma District, and on the western shores of Lake Tanganyika at Kalemie in the D.R. Congo (Capart 1952).

Ecology
Little is known about the habitat and ecology of P. amosae sp. nov. In the region of Lake Tanganyika this species was often captured in marshes and wetlands near the lake, but never in the lake itself (Capart 1952). In Lake Kivu this species is found on islands in the lake as well as in the lake (Chace 1942). The range of P. amosae sp. nov. includes part of the Lake Victoria Basin Freshwater Ecoregion (FEOW #521) (Thieme et al. 2005;Abell et al. 2008).

Conservation status
An IUCN extinction risk assessment of P. amosae sp. nov. has not yet been carried out. This species has a wide distributional range (with an estimated extent of occurrence (EOO) of almost 46 600 km 2 ) and has been recorded from seven localities (Fig. 3) in three different countries. Given that there are no known immediate threats to this species, it would probably be assessed as Least Concern.

Remarks
There are a number of characters that distinguish P. amosae sp. nov. from P. orbitospinus in Lake Malawi. For example, the male thoracic sternal sulcus S3/4 of P. amosae sp. nov. is faint and shallow (vs deep and complete in P. orbitospinus); the low dorsal lobe of the G1 TA of P. amosae sp. nov. means that it is only slightly widened (vs a G1 TA dorsal margin that is conspicuously widened by a high dorsal lobe in P. orbitospinus); the anterolateral margin of P. amosae sp. nov. is lined by small granules (vs lined by a row of small distinct teeth in P. orbitospinus); the merus, propodus, and dactylus of P5 of P. amosae sp. nov. are all short (vs all elongated and slender in P. orbitospinus); and the third maxilliped ischium of P. amosae sp. nov. is smooth (vs with a third maxilliped ischium that has a deep vertical sulcus in P. orbitospinus).
In the past, P. amosae sp. nov. from Lake Kivu has been identifi ed as P. lirrangensis s. lat. by a number of authors (Chace 1942;Bott 1955;Reed & Cumberlidge 2006;Cumberlidge & Meyer 2011). These identifi cations were made based on characters shared with the type of P. lirrangensis s. str. from Liranga (such as denticles or granules lining the anterolateral margin, 2 large pointed spines on the cheliped carpus inner margin, and a large pointed spine on the cheliped merus inner margin). There are a number of illustrations of P. amosae sp. nov. available, but most of these specimens have been identifi ed as P. lirrangensis s. lat. For example, Chace (1942) illustrated the carapace and G1 of a specimen from Lake Kivu (MCZ CRU-11224), and Capart (1952: fi g. 12) fi gured an entire specimen from Kalemie (formerly Albertville) on the western shores of Lake Tanganyika and remarked on its similarity to the species found in Lake Kivu. Later, Reed & Cumberlidge (2006: fi gs 41-51, 153-154, 177 pl. V) described in detail an adult female (CW 81 mm) and male (CW 56.5 mm) of P. lirrangensis s. lat. (NMU TRW1971.15) from the Malagarasi River at Uvinza in the Kigoma District of Tanzania near Lake Tanganyika.
DNA sequence data are available from specimens formerly assigned to P. lirrangensis s. lat. from Lakes Kivu, Tanganyika, and Malawi Daniels et al. 2015;Kochey et al. 2017). Marijnissen et al. (2006) used 2 mitochondrial DNA sequence markers (12S rRNA and 16S rRNA) to investigate relationships between specimens identifi ed morphologically as P. lirrangensis s. lat. from Ruzizi in Lake Kivu in the D.R. Congo (GenBank DQ203210, DQ203236), from Uazua in the Zambian part of Lake Tanganyika (DQ203211, DQ203237), and from Thumbi West Island near Cape Maclear in southern Lake Malawi (GenBank DQ203209, DQ203235). Marijnissen et al. (2006: fi g. 1) found that the specimen from Lake Kivu (here recognised as P. amosae sp. nov.) formed a separate basal lineage from the clade formed by the other 2 specimens from Lake Malawi (here recognised as P. orbitospinus). Daniels et al. (2015) sequenced four DNA markers (GenBank AY803494, AY803534, AY803568, AY803682) for a specimen (ZMA.Crust.De.204681) held in the NBL that was identifi ed in that work as P. lirrangensis s. lat. and incorrectly listed as being from Lake Malawi. In fact, specimen ZMA.Crust. De.204681 was collected from Lake Kivu (site 13, E. major; 23 Aug. 2002; Pascal Isumbisa leg.) and is therefore properly identifi ed as P. amosae sp. nov.

Common name
The Malawi blue crab.

Size
Large species, pubertal molt starting around CW 53 mm (largest adult male CW 56.9 mm, largest adult female CW 53.9 mm).

Colour
The carapace surface and branchiostegal walls of living specimens are deep blue, and are especially bright in newly-hardened specimens (Fig. 13). There are distinct white outlines marking the postfrontal crest, anterolateral margins, frontal margin, orbital margins, exorbital teeth, epistome, and the third maxilliped ischium and merus. The thoracic sternum is pinkish blue/grey and cream, and the arthrodial membranes on the inner side of the joints between the coxae and the basis of the chelipeds and P2-5 are cream.

Distribution
Potamonautes orbitospinus is abundant and widely distributed throughout Lake Malawi (Fig. 2) and has not been recorded from outside of the lake.

Ecology
Lake Malawi is the southernmost Great Lake in the East African Rift system and lies in 3 countries: Malawi, Mozambique, and Tanzania. The Ruhuhu River in Tanzania fl ows west into the northeastern part of Lake Malawi while the Shire River drains south out of the lake and is a tributary of the Zambezi River. Fig. 13. Potamonautes orbitospinus (Cunnington, 1907), living specimen from Lake Malawi, Malawi. Photograph Oliver-Mengedoht.de/Panzerwelten.de.
In 1904, Cunnington and his assistants collected the fi rst known specimens of P. orbitospinus from the waters of Lake Malawi itself, noting that some specimens were found on the beach (Cunnington 1907). The specimens reported on here are all restricted to Lake Malawi, and this species is a lake specialist that has never been collected in the rivers of the drainage basin that fl ow into the lake.

Conservation status
An IUCN conservation assessment of P. orbitospinus has not yet been carried out. The species is known from a large number of specimens from 16 localities all in Lake Malawi (29 600 km 2 ). Given that its estimated extent of occurrence (EOO) is more than 21 100 km 2 , and that no specifi c threats are known, it would probably be assessed as Least Concern. It is signifi cant that the population levels of P. orbitospinus are suffi cient to be regularly caught as bycatch in local fi sheries in Lake Malawi, and this species is also captured to supply a steady demand by the global aquarium trade.

Remarks
The recognition of P. orbitospinus and P. lirrangensis s. str. as valid species returns to the original taxonomic situation over 110 years ago when they were fi rst described from two widely separated locations (Rathbun 1904;Cunnington 1907). Chace (1942) also treated P. lirrangensis and P. orbitospinus as valid species, but Bott (1955), Reed & Cumberlidge (2006) and Cumberlidge & Meyer (2011) considered Potamon (Potamonautes) orbitospinus to be a junior synonym of Potamonautes lirrangensis s. lat. The result has been that the available descriptions and distribution maps of Potamonautes lirrangensis s. lat. (Reed & Cumberlidge 2006: fi g. 177) incorrectly combine characters and localities of P. lirrangensis s. str. from the Congo River with those of P. orbitospinus from Lake Malawi, and P. amosae sp. nov. from Lake Kivu and Kigoma District near Lake Tanganyika.
Potamonautes orbitospinus is recognised here based on characters of the lectotype described by Cunnington (1907) from Lake Malawi as well as other comparable material from this lake. The redescription includes new taxonomically important characters because although the description by Cunnington (1907) of P. orbitospinus was based on an adult male, he did not illustrate the fi rst gonopod or sternal characters of the type specimen. See concluding remarks below for comparisons with other superfi cially similar species.
The combined phylogeny based on mitochondrial 16S rRNA and the nuclear coding gene Histone H3 (Fig. 14) includes a specimen from Thumbi West Island near Cape Maclear in southern Lake Malawi (GenBank DQ203209, DQ203235), alongside eight other specimens from Cape Maclear and Chiofu on the east coast of Lake Malawi. The phylogeny suggests a monophyletic clade for P. orbitospinus from Lake Malawi, separate from the clade for P. amosae sp. nov. (Fig. 14).
A specimen identifi ed as P. lirrangensis s. lat. from 'Uazua' in the Zambian part of Lake Tanganyika (POlirrangensisZAM31; Marijnissen et al. 2006) has a partial 16S sequence (DQ203237) with high similarity (99%) to a specimen of P. orbitospinus from Lake Malawi (POlirrangensisMAL27; DQ203235; Marijnissen et al. 2006). This same specimen (POlirrangensisZAM31), however, has a partial 12S sequence (DQ203211) which has only 97% similarity to POlirrangensisMAL27 (DQ203209). This may indicate that P. orbitospinus shares a close evolutionary affi nity to specimens within Lake Tanganyika, but further sampling is required to determine the evolutionary relationships of these two groups. Kochey et al. (2017) carried out a molecular study of the Malawi blue crab (which they identifi ed as P. lirrangensis s. lat.) that found the morphologically similar populations in Lake Malawi to be equally close genetically, and confi rmed that the lake hosts only a single species of freshwater crab (here identifi ed as P. orbitospinus). Those authors also found that the blue crab populations in Lake Malawi had only moderate haplotype diversity and low levels of nucleotide diversity for two mitochondrial loci (NADH dehydrogenase subunit 1 (ND1) and cytochrome b (CytB) (Kochey et al. 2017). The lack of divergence of blue crab populations in Lake Malawi and the morphological similarity of specimens found in different parts of the lake suggests a recent colonisation (Kochey et al. 2017).

Discussion
The results of the present molecular study (Fig. 14) support the recognition of P. orbitospinus from Lake Malawi and of P. amosae sp. nov. from Lake Kivu and Tanzania. The 4 taxa formerly assigned to Potamonautes orbitospinus (Cunnington, 1907) and P. amosae sp. nov. were both formerly included in the Potamonautes lirrangensis (Rathbun, 1904) s. lat. species complex. The analysis combines 16SrRNA (489 bp alignment) and Histone 3 sequences (290 bp alignment). Numbers above branches indicate Bayesian Inference (~BI) posterior probability support values, and numbers below branches indicate Maximum likelihood (ML) bootstrap support values. Only intraspecifi c node support values are shown for clarity. '-' indicates the node was not supported by ML analysis. Codes on the branch tips indicate either isolate numbers or *Genbank accession numbers (Table 2). Other species shown on the tree (P. bellarussus Daniels, Phiri & Bayliss, 2014, P. choloensis Chace, 1953, P. obesus A. Milne-Edwards, 1868, and P. cf. unispinus Stewart & Cook, 1998) have a distribution that overlaps with that of the focal species (P. lirrangensis s. lat.). The outgroup species is Sudanonautes fl oweri de Man, 1901 from Cameroon and Gabon. The scale bar indicates genetic distance. P. lirrangensis s. lat., namely P. lirrangensis s. str. from Liranga, P. kisangani sp. nov. from Kisangani, P. orbitospinus from Lake Malawi, and P. amosae sp. nov. from Lake Kivu and Tanzania, can be distinguished by the suite of morphological characters provided earlier.
The present study has resolved a long-standing controversy regarding the taxonomic identity of the Malawi blue crab, which was formerly identifi ed as P. lirrangensis s. lat., and, after 65 years, is now again recognized as P. orbitospinus. In addition, the identity of the largest species of freshwater crab found in Lake Kivu is recognized here as P. amosae sp. nov. and this is grouped with populations of large crabs from the Lake Tanganyika drainage in Tanzania and the D.R. Congo. Finally, a better understanding of the taxonomic status of P. lirrangensis s. str. from Liranga and P. kisangani sp. nov. from Kisangani await further collections from the largely unexplored Middle Congo River.